1. Field of the Invention
The present invention relates generally to wireless communication systems, and in particular to establishing a connection between user equipment and an associated network.
2. Discussion of the Related Art
A universal mobile telecommunication system (UMTS) is a European-type, third generation IMT-2000 mobile communication system that has evolved from a European standard known as global system for mobile communications (GSM). UMTS is intended to provide an improved mobile communication service based upon a GSM core network and wideband code division multiple access (W-CDMA) wireless connection technology.
In December 1998, a Third Generation Partnership Project (3GPP) was formed by the ETSI of Europe, the ARIB/TTC of Japan, the T1 of the United States, and the TTA of Korea. The 3GPP creates detailed specifications of UMTS technology. In order to achieve rapid and efficient technical development of the UMTS, five technical specification groups (TSG) have been created within the 3GPP for standardizing the UMTS by considering the independent nature of the network elements and their operations.
Each TSG develops, approves, and manages the standard specification within a related region. Among these groups, the radio access network (RAN) group (TSG-RAN) develops the standards for the functions, requirements, and interface of the UMTS terrestrial radio access network (UTRAN), which is a new radio access network for supporting W-CDMA access technology in the UMTS.
FIG. 1 gives an overview of the UMTS network, including the UE, the UTRAN and the core network. The UTRAN is composed of several radio network controllers (RNCs) and Node-Bs, which communicate via the Iub interface.
Each RNC controls several Node-Bs. Each RNC is connected via the Iu interface to the core network (CN), specifically to the MSC (mobile-services switching center) and the SGSN (serving GPRS support node) of the CN. RNCs can be connected to other RNCs via the Iur interface. The RNC handles the assignment and management of radio resources and operates as an access point with respect to the core network.
The Node-Bs receive information sent by the physical layer of the terminal through an uplink transmission and transmit data to the terminal through a downlink transmission. The Node-Bs operate as access points of the UTRAN for the terminal.
The SGSN is connected via the Gf interface to the EIR (equipment identity register), via the GS interface to the MSC, via the GN interface to the GGSN (gateway GPRS support node) and via the GR interface to the HSS (home subscriber server). The EIR maintains lists of mobiles that are allowed to be used on the network.
The MSC, which controls the connection for circuit switch (CS) services. The MSC is connected to the MGW (media gateway) via the NB interface, to the EIR via the F interface, and to the HSS via the D interface. The MGW is connected to the HSS via the C interface and to the PSTN (Public Switched Telephone Network). The MGW facilitates adapting the codecs between the PSTN and the connected RAN.
The GGSN is connected to the HSS via the GC interface, and to the Internet via the GI interface. The GGSN is responsible for routing, charging, and separation of data flows into different radio access bearers (RABs). The HSS handles the subscription data of the users.
The UTRAN constructs and maintains a radio access bearer (RAB) for communication between the terminal and the core network. The core network requests end-to-end quality of service (QoS) requirements from the RAB, and the RAB supports the QoS requirements set by the core network. Accordingly, the UTRAN can satisfy the end-to-end QoS requirements by constructing and maintaining the RAB.
The services provided to a specific terminal are roughly divided into circuit switched services and packet switched services. For example, a general voice conversation service is a circuit switched service, while a Web browsing service via an Internet connection is classified as a packet switched service.
For supporting circuit switched services, the RNCs are connected to the mobile switching center (MSC) of the core network, and the MSC is connected to the gateway mobile switching center (GMSC) which manages the connection with other networks. For supporting packet switched services, the RNCs are connected to the serving general packet radio service (GPRS) support node (SGSN), and the gateway GPRS support node (GGSN) of the core network. The SGSN supports the packet communications with the RNCs, and the GGSN manages the connection with other packet switched networks, such as the Internet.
FIG. 2 illustrates a structure of a radio interface protocol between the terminal and the UTRAN according to the 3GPP radio access network standards. As shown in FIG. 2, the radio interface protocol has vertical layers comprising a physical layer, a data link layer, and a network layer, and has horizontal planes comprising a user plane (U-plane) for transmitting user data and a control plane (C-plane) for transmitting control information.
The user plane is a region that handles traffic information with the user, such as voice or Internet protocol (IP) packets. The control plane is a region that handles control information for an interface with a network, maintenance and management of a call, and the like.
The protocol layers in FIG. 2 can be divided into a first layer (L1), a second layer (L2), and a third layer (L3) based on the three lower layers of an open system interconnection (OSI) standard model. The first layer (L1), or the physical layer, provides an information transfer service to an upper layer by using various radio transmission techniques. The physical layer is connected to an upper layer, called a medium access control (MAC) layer, via a transport channel.
The MAC layer and the physical layer exchange data via the transport channel. The second layer (L2) includes a MAC layer, a radio link control (RLC) layer, a broadcast/multicast control (BMC) layer, and a packet data convergence protocol (PDCP) layer.
The MAC layer handles mapping between logical channels and transport channels, and provides allocation of the MAC parameters for allocation and re-allocation of radio resources. The MAC layer is connected to an upper layer, called the radio link control (RLC) layer, via a logical channel.
Various logical channels are provided according to the type of information transmitted. In general, a control channel is used to transmit information of the control plane, and a traffic channel is used to transmit information of the user plane.
A logical channel may be a common channel or a dedicated channel depending on whether the logical channel is shared. Logical channels include a dedicated traffic channel (DTCH), a dedicated control channel (DCCH), a common traffic channel (CTCH), a common control channel (CCCH), a broadcast control channel (BCCH), and a paging control channel (PCCH) or a shared channel control channel.
The BCCH provides information including information utilized by a terminal to access a system. The PCCH is used by the UTRAN to access a terminal.
For the purposes of a multimedia broadcast/multicast service (MBMS) additional traffic and control channels are introduced in the MBMS standard. The MCCH (MBMS point-to-multipoint control channel) is used for transmission of MBMS control information. The MTCH (MBMS point-to-multipoint traffic channel) is used for transmitting MBMS service data. The MSCH (MBMS Scheduling Channel) is used to transmit scheduling information. The different logical channels that exist are listed in FIG. 3.
The MAC layer is connected to the physical layer by transport channels and can be divided into a MAC-b sub-layer, a MAC-d sub-layer, a MAC-c/sh sub-layer, a MAC-hs sub-layer and a MAC-m sublayer according to the type of transport channel being managed. The MAC-b sub-layer manages a BCH (broadcast channel), which is a transport channel handling the broadcasting of system information. The MAC-c/sh sub-layer manages a common transport channel, such as a forward access channel (FACH) or a downlink shared channel (DSCH), which is shared by a plurality of terminals, or in the uplink the radio access channel (RACH). The MAC-m sublayer may handle the MBMS data.
The possible mapping between the logical channels and the transport channels from a UE perspective is given in FIG. 4. The possible mapping between the logical channels and the transport channels from a UTRAN perspective is given in FIG. 5.
The MAC-d sub-layer manages a dedicated channel (DCH), which is a dedicated transport channel for a specific terminal. The MAC-d sublayer is located in a serving RNC (SRNC) that manages a corresponding terminal. One MAC-d sublayer also exists in each terminal.
The RLC layer, depending of the RLC mode of operation, supports reliable data transmissions and performs segmentation and concatenation on a plurality of RLC service data units (SDUs) delivered from an upper layer. When the RLC layer receives the RLC SDUs from the upper layer, the RLC layer adjusts the size of each RLC SDU in an appropriate manner based upon processing capacity and then creates data units by adding header information thereto. The data units, called protocol data units (PDUs), are transferred to the MAC layer via a logical channel. The RLC layer includes a RLC buffer for storing the RLC SDUs and/or the RLC PDUs.
The BMC layer schedules a cell broadcast (CB) message transferred from the core network and broadcasts the CB message to terminals positioned in a specific cell or cells.
The PDCP layer is located above the RLC layer. The PDCP layer is used to transmit network protocol data, such as the IPv4 or IPv6, effectively on a radio interface with a relatively small bandwidth. For this purpose, the PDCP layer reduces unnecessary control information used in a wired network, a function called header compression.
The radio resource control (RRC) layer located at the lowest portion of the third layer (L3) is only defined in the control plane. The RRC layer controls the transport channels and the physical channels in relation to setup, reconfiguration, and the release or cancellation of the radio bearers (RBs). Additionally the RRC handles user mobility within the RAN and additional services, such as location services.
The RB signifies a service provided by the second layer (L2) for data transmission between the terminal and the UTRAN. In general, the set up of the RB refers to the process of stipulating the characteristics of a protocol layer and a channel required for providing a specific data service, and setting the respective detailed parameters and operation methods.
The different possibilities that exist for the mapping between the radio bearers and the transport channels for a given UE are not all possible all the time. The UE and UTRAN deduce the possible mapping depending on the UE state and the procedure that the UE and UTRAN are executing. The different states and modes are explained in more detail below, as far as they concern the present invention.
The different transport channels are mapped onto different physical channels. For example, the RACH transport channel is mapped on a given PRACH, the DCH can be mapped on the DPCH, the FACH and the PCH can be mapped on the S-CCPCH, and the DSCH is mapped on the PDSCH. The configuration of the physical channels is given by RRC signaling exchange between the RNC and the UE.
The RRC mode refers to whether there exists a logical connection between the RRC of the terminal and the RRC of the UTRAN. If there is a connection, the terminal is said to be in RRC connected mode. If there is no connection, the terminal is said to be in idle mode.
Because an RRC connection exists for terminals in RRC connected mode, the UTRAN can determine the existence of a particular terminal within the unit of cells. For example, the UTRAN can determine in which cell or set of cells an RRC connected mode terminal is located and to which physical channel the UE is listening. Thus, the terminal can be effectively controlled.
In contrast, the UTRAN cannot determine the existence of a terminal in idle mode. The existence of idle mode terminals can only be determined by the core network to be within a region that is larger than a cell, for example, a location or a routing area. Therefore, the existence of idle mode terminals is determined within large regions, and in order to receive mobile communication services such as voice or data, the idle mode terminal must move or change into the RRC connected mode. The possible transitions between modes and states are shown in FIG. 6.
A UE in RRC connected mode can be in different states, such as CELL_FACH state, CELL_PCH state, CELL_DCH state, or URA_PCH state. Depending on the state, the UE carries out different actions and listens to different channels.
For example, a UE in CELL_DCH state will try to listen to DCH type of transport channels, among others. DCH types of transport channels include DTCH and DCCH transport channels, which can be mapped to a certain DPCH, DPDSCH or other physical channels.
The UE in CELL_FACH state will listen to several FACH transport channels, which are mapped to a certain S-CCPCH. A UE in PCH state will listen to the PICH channel and the PCH channel, which are mapped to a certain S-CCPCH physical channel.
The main system information is sent on the BCCH logical channel which is mapped on the P-CCPCH (primary common control physical channel). Specific system information blocks can be sent on the FACH channel. When the system information is sent on FACH, the UE receives the configuration of the FACH either on the BCCH that is received on P-CCPCH or on a dedicated channel. When system information is sent on the BCCH (i.e,. via the P-CCPCH), then in each frame or set of two frames the SFN (system frame number) is sent which is used in order to share the same timing reference between the UE and the Node-B. The P-CCPCH is sent using the same scrambling code as the P-CPICH (primary common pilot channel), which is the primary scrambling code of the cell. The spreading code that is used by the P-CCPCH is of a fixed SF (spreading factor) 256, and the number is one. The UE knows about the primary scrambling code either by information sent from the network on system information of neighboring cells that the UE has read, by messages that the UE has received on the DCCH channel, or by searching for the P-CPICH, which is sent using the fixed SF 256, the spreading code number 0 and which transmits a fixed pattern.
The system information comprises information on neighboring cells, configuration of the RACH and FACH transport channels, and the configuration of MICH and MCCH which are channels that are dedicated channels for the MBMS service.
Each time the UE changes the cell it is camping (in idle mode) or when the UE has selected the cell (in CELL_FACH, CELL_PCH or URA_PCH) state, the UE verifies that it has valid system information. The system information is organized in SIBs (system information blocks), a MIB (master information block) and scheduling blocks. The MIB is sent very frequently and gives timing information of the scheduling blocks and the different SIBs. For SIBs that are linked to a value tag, the MIB also contains information on the last version of a part of the SIBs. SIBs that are not linked to a value tag are linked to an expiration timer. SIBs linked to an expiration timer become invalid and need to be reread if the time of the last reading of the SIB is larger than this timer value. SIBs linked to a value tag are only valid if they have the same value tag as the one broadcast in the MIB. Each block has an area scope of validity (cell, PLMN, equivalent PLMN) which signifies on which cells the SIB is valid. A SIB with area scope “cell” is valid only for the cell in which it has been read. A SIB with area scope “PLMN” is valid in the whole PLMN, a SIB with the area scope “equivalent PLMN” is valid in the whole PLMN and equivalent PLMN.
In general UEs read the system information when they are in idle mode, CELL_FACH state, CELL_PCH state or in URA_PCH state of the cells that they have selected or the cell that they are camping on. In the system information, they receive information on neighboring cells on the same frequency, different frequencies and different RAT (radio access technologies). This allows the UE to know which cells are candidates for cell reselection.
MBMS is introduced in the UMTS standard in the Release 6 of the specification (Rel-6). It describes techniques for optimized transmission of MBMS bearer service including point-to-multipoint transmission, selective combining and transmission mode selection between point-to-multipoint and point-to-point bearers. This is used in order to save radio resources when the same content is sent to multiple users, and enables TV-like services. MBMS data can be split into two categories, control plane information and user plane information. The control plane information contains information on the physical layer configuration, transport channel configuration, radio bearer configuration, ongoing services, counting information, scheduling information, and the like. In order to allow UEs to receive this information, MBMS bearer specific control information for the MBMS is sent to the UEs.
The user plane data of MBMS bearers can be mapped onto dedicated transport channels for a point-to-point service which is sent only to one UE, or on a shared transport channel for point to multipoint service which is transmitted to (and received by) several users at the same time.
Point-to-point transmission is used to transfer MBMS specific control/user plane information, as well as dedicated control/user plane information between the network and a UE in RRC connected mode. It is used for the multicast or the broadcast mode of MBMS. DTCH is used for a UE in CELL_FACH and Cell_DCH. This allows existing mappings to transport channels.
To allow cell resources to be used in an optimized manner, a function called counting has been introduced in MBMS applications. The counting procedure is used to determine how many UEs are interested in the reception of a given service. This is done by using the counting procedure shown in FIG. 7.
For example, a UE that is interested in a certain service receives information of the availability of a MBMS service. The network can inform the UE that it should indicate to the network its interest in the service in the same way such as by transmitting the “access information” on the MCCH channel. A probability factor included in the access information message determines that an interested UE will only respond with a given probability. In order to inform the network that the UE is interested in a given service, the UE will send to the network the RRC connection setup message or the cell update message in the cell that the UE has received the counting information. This message may potentially include an identifier indicating the service that the UE is interested in.
Point-to-multipoint transmission is used to transfer MBMS specific control/user plane information between the network and several UEs in RRC connected or idle mode. It is used for broadcast or multicast mode of MBMS.
In the case that the network operates on several frequencies, when a UE is camping on one frequency, and a MBMS service is transmitted on a different frequency, a UE may not be aware of the fact that a MBMS service is transmitted in the different frequency. Therefore the frequency convergence procedure allows the UE to receive information in frequency A that indicates in a frequency B that a given service is available.